(No.7 Geological Brigade of Henan Nonferrous Metals Bureau of Geology and Mineral Resources)
Mineral resources are the foundation for the survival and development of human society, and ensuring the stable supply of mineral resources is the basic condition for the sustainable development of the national economy. Premier Wen Jiabao has repeatedly stressed that "we should attach great importance to the sustainable development and utilization of mineral resources and take it as the main strategic task".
First, the status quo of mining development in China
In recent 20 years, China has entered the stage of rapid development of national economy, and the consumption of mineral resources has increased rapidly. The existing resource reserve is far from meeting the growing demand, and it has reached an unsustainable development situation of "making ends meet". According to the prediction of relevant experts, by 2020, the demand for mineral products in China will double again, while the reserves of 45 major mineral resources in China can only meet the demand of 1/3. Without new resource reserves, bulk mineral products will mainly rely on imports and will surpass the United States to become the world's largest importer of mineral products.
Although economic globalization and diversification have provided favorable channels for China to import mineral resources, the forces of hegemonism and restraining China's "peaceful rise" are still strong, and the merger and reorganization of multinational corporations have intensified the global monopoly of mineral resources and seriously threatened the security of China's resource security system. What is more serious is that two thirds of the more than 600 large and medium-sized mines in China have entered the middle and late stage of mining, and the reserve resources are seriously insufficient. In recent years, a large number of industrial workers have been laid off due to the closure or conversion of mines, which has greatly increased the social burden and unstable factors. If new reserve resources cannot be provided as soon as possible, the problem of "four mines" will seriously restrict the sustained, stable and rapid development of the national economy.
Second, the urgency of deep prospecting work
Ensuring the sustainable supply of mineral resources has become an important long-term strategic task for the country. On June 65438+1October 65438+May, 2002, Premier Wen Jiabao pointed out at the 50th anniversary commemorative meeting of geological work in China that "efforts should be made to find new replacement resources around or deep in the old mines with market demand and resource potential". The main problems faced by China's mineral resources replacement base are: it is difficult to explore the deep part of old mines and various concealed areas, and it is urgent to guide deep prospecting with new theories and new technical methods of metallogeny and metallogenic prediction. Deep prospecting prediction has become the scientific frontier and research hotspot of mineralization and metallogenic prediction.
At present, most of China's metal mines are located in areas with relatively good topographic conditions, and the exploration and mining depths are all above 500m. However, below 500 m, due to the complex geological and structural environment, it is more difficult to find minerals, and the original detection instruments have low resolution and lack of effective means and methods, which seriously affects the exploration and development of deep resources. In recent years, with the breakthrough of metallogenic theory research and the application of new technologies and methods, large and super-large deposits have been discovered in the depth of 500 ~ 2000 m underground, which shows that there are huge potential mineral resources in Chinese mainland. How to accurately and effectively predict the deep location has become an urgent and important research task.
Third, optimize the target area and attack in depth to find blindness.
As a geological prospecting unit, we must be anxious about the urgent needs of the country and take it as our responsibility to find the mineral resources that the country urgently needs. After the topic of "Comprehensive Exploration and Deep Prospecting" was put forward, after careful screening, our team chose Shute Nuoer silver-lead mine in Abaga Banner, Inner Mongolia, which has great potential for deep prospecting, as one of the breakthroughs, to give full play to our comprehensive technical advantages of geophysical and geochemical exploration and carry out deep prediction research of concealed ore.
(1) Geological background
The structural position of the mining area belongs to the middle section of the arc fold belt in Inner Mongolia, which is located in the northwest wing of anticlinorium in Qaidam. It belongs to the Cu-Mo-Pb-Zn-Fe metallogenic belt in the north of Daxing 'anling, which is spatially consistent with the Late Paleozoic accretionary orogenic belt in the northeast of the north of Daxing 'anling. It is located in the northwest plate of Erlian-Hagenshan tectonic belt and the south plate of Delbays fault zone, extending northward to the Russian Far East, being intercepted by the Mongolia-Okhotsk tectonic belt, and at the same time entering Mongolia to connect with its southwestern South Gobi metallogenic province (Figure 1).
Figure 1 geotectonic map of Shute Nuoer, Inner Mongolia
Chagan Subul Jia and Ouyu Tolgoi porphyry Cu-Au-Mo deposits were discovered in the south Gobi of Mongolia in the southwest extension of the ore belt. Controlled by NW-SE compressive stress of North China plate and Siberia plate, the structures in this area are extremely developed, mainly NE-trending faults and NW-trending faults. The NE-trending faults are large-scale compressive faults, which control the distribution of intrusive rocks in the later period, while the NW-trending and EW-trending faults are small-scale faults, which control the distribution of dikes, tectonic mineralization alteration zones and mineralization fracture zones in the later period.
The exposed strata in the mining area include the Lower Devonian Aobaoting Hundi Formation (D 1a), the Lower Permian Baolige Formation (P 1b) and the Quaternary (Q). The rocks are mainly some eruptive pyroclastic rocks, including carbonaceous, silty slate and sandstone.
The structure in the area is extremely developed, with Hemuta Aobao fault and Sendu Wendell compression belt passing through the mining area in the northeast direction, and the Qaidam fault in the southeast extending in the northeast direction. On the southeast side, the Erlian-Hegenshan fault runs in the northeast direction.
In addition to the above three major faults, NE and NW faults can also be seen in the mining area, which are generally ring-shaped torsion structures. The NE-trending fault is a large-scale compressive fault, which provides a channel for the migration of ore-forming materials. The NW-trending and EW-trending faults are tensile and torsional faults, which provide the occurrence space for the formation of ore bodies in this area.
Magmatic rocks in the mining area are exposed in the northwest and southwest, mainly Indosinian granite (γ 15), which is controlled by the NE-SW regional tectonic line, with bedrock occurrence and simple intrusion stage, and all belong to Indosinian intrusion. Mainly granite and biotite granite, medium-fine to fine-grained porphyritic structure, medium-grained or unequal-grained structure locally. The mainstream structure in the rock mass is not obvious, and the derived dikes are not developed. The northern part of the rock mass is in fault contact and intrusive contact with the lower Permian Baolige Formation (P 1b), forming a thermal metamorphic belt (mainly porphyry) with a width of tens of meters. The metamorphic sandstone of the Lower Devonian Aobaohundi Formation (D 1a) was invaded in the south, forming actinolite amphibole belt and porphyry belt with a width of100 ~ 200 m..
Veins are developed in this area, which can be divided into regional veins and derived veins according to their lithologic characteristics and distribution characteristics. The former is controlled by later faults and fractures, and the latter is mostly controlled by primary joints of rock mass, which are distributed near the rock mass and its marginal contact zone. The dikes in the mining area are mainly Indosinian intrusive dikes, including granite porphyry (γ π), quartz porphyry (qπ), diorite dike (δ) and quartz dike (Q). Most dikes are NW-trending, and a few dikes are NE-trending, invading the Lower Devonian Aobaohundi Formation (D 1a) and the Lower Permian Baolige Formation (P6
Because Indosinian granite contains high copper content and is rich in copper-loving elements, and the mining area is located in the outer contact zone of granite, hydrothermal activity and dike rocks are widely distributed in the later period, magmatism in this area is more conducive to mineralization.
(2) Put forward the idea of "geological and physical anomalies cooperate with each other" to locate and predict concealed ore. Through the combination of geophysical technology and scientific workflow, remarkable results have been achieved in the prospecting of lead-zinc mine in Hadatetolgoi.
Concealed metal ore-forming element rich body (i.e. mineralized body) is a part of the earth's crust, which has some physical properties different from those of surrounding rocks and constitutes relatively independent physical anomalies, which is the basic basis for various technical methods to determine geological and geophysical anomalies. At present, the combined application of gravity, magnetic and electric methods can not only delineate the approximate range of anomalies, but also accurately delineate the boundary and depth of hidden anomalies. Therefore, under the current technical level, the target of location prediction of concealed ore should be not only geological structure beneficial to mineralization, but also geophysical anomalies, which is the best exploration target of concealed ore. The expected exploration target should be mainly the concealed mineralization alteration zone, and of course it may also be the ore body.
Hadatetolgoi lead-zinc mine is located in the east of Shutenor silver-lead mine, which belongs to the same structural unit as Shutenor silver-lead mine. Strata, structure and magmatic rocks are basically the same, and the surface is covered by Quaternary. According to the parameter data of Hadate mining area (table 1), there is obvious electrical difference between the mineralized altered fractured rock and the surrounding rock, which has the premise of direct prospecting for mineralized bodies by geophysical and geochemical exploration and electrical method, and its electrical characteristics are high resistance and high polarization. This feature is related to the mineralization phenomenon in this survey area, which is characterized by high silicification and strong alteration.
Table 1 electrical parameter test table of rock samples
Many IP anomalies have been found in the lead-zinc mine area of Hadatetolgoi, among which IP7 IP anomaly is located in the southwest corner of the mining area, and the anomaly is distributed in the northwest direction, with a length of 503m and a width of 275m. The two ends are not closed, and the anomaly shape is complete, and the concentration center is obvious (Figure 2).
IP sounding is arranged at the point 142 # ~ 176 # where IP7 is abnormal. When AO=400m is shallow, there are three steep high polarizability anomalies at 154#, 160# and 168#, which correspond to high resistivity. At the depth of AO=400m, three shallow anomalies are combined, indicating that there are high-resistivity and high-polarization anomalies in the deep (Figure 3).
The borehole ZK7- 1 and ZK7-2 verify that the prospecting effect is good, and it is determined that the IP7 anomaly is a mine-caused anomaly.
(C) Broad prospects
(1) Up to now, 60 boreholes have been drilled in the lead-zinc mine area of Hadatetolegai, with a footage of more than 23,000 meters, more than 80% of which have been mined, and more than 65,438+10,000 tons of lead and zinc resources have been obtained.
Fig. 2 abnormal IP 7 diagram
Fig. 3 Pseudo-profile of IP sounding in 7 # exploration line
(2) After the previous geological and geophysical work, seven IP anomalies were found in Shuternuoer silver-lead mining area. Borehole inspection was carried out in 2008, and it was found that the cumulative thickness of lead-zinc mine was 5.55m, and two lead-zinc polymetallic ore bodies were delineated by * * *, totaling (334)? Lead and zinc resources are 39,700 t, and silver (334)? The resource amount is11.4t. The prospect is very promising.
(3) The buried depth of ore bodies found in the two mining areas is more than 500 meters, and geophysical anomalies show that there are anomalies below 500 meters, which has great prospecting potential. At present, our team is carrying out geophysical exploration such as transient electromagnetic and high-precision magnetic survey in this mining area, which provides an important means for our team to find deep polarizers in Hadate area of Xilin Gol League, Inner Mongolia.
Deep prospecting is a challenging job, and it faces many difficulties. We should carry forward the glorious tradition of the geological prospecting team and face the difficulties. Guided by the frontier metallogenic theory and metallogenic prediction theory, combined with geophysical and geochemical exploration methods, we will strengthen the comprehensive research of data and strive to make a big breakthrough in the second metallogenic space. Our technical strength is limited, so we urge the Ministry of Geology and Mineral Resources and the Ministry of Science and Technology to provide more technical support and guidance to help us carry out our work better.